The present invention relates to the manufacture of semiconductor devices and more particularly to the baking of photosensitive resists used for forming patterns on the faces of semiconductor wafers.
The baking of photosensitive resist coatings on semiconductor wafers has heretofore been performed in essentially conventional oven structures. For example, wafers are either inserted in a batch convection oven or have been carried on a flexible band through a tunnel oven where the wafers have been gradually heated by the ambient temperature in the oven. During the baking, solvents are driven off from the resist and the resist is cured. As the resist typically cures from the outside in, the baking must occur relatively slowly. Otherwise, "skinning" can occur, i.e. when the outer surface cures or dries with underlying resist being uncured. As is understood by those skilled in the art, this can lead to so-called "pinholing" where small holes are formed in the resist coating by the escape of entrapped heat-generated gases.
As a result of the above-identified problems, conventional wisdom in the semiconductor art has held that a typical photoresist must be cured at a modest temperature (85.degree.-95.degree. C.) and for relatively long times (3-30 minutes). As a consequence, the oven structures typically employed in semiconductor manufacturing systems have been relatively large since they must hold the wafers for a significant amount of time and, given the rate at which other processes can proceed, a relatively large number of wafers will be undergoing baking at any one time. As is also understood by those skilled in the art, this large size or volume imposes a significant economic floorspace penalty in the context of "clean room" operations such as are required for semiconductor manufacture.
Among the several objects of the present invention may be noted the provision of apparatus for quickly baking photosensitive resist on semiconductor wafers; the provision of such apparatus which requires relatively small space in a semiconcuctor manufacturing line; the provision of such apparatus which effects a uniform cure of the photoresist; the provision of such apparatus which effects curing without skinning or pinholing; the provision of such apparatus which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.